Coil form adapted for use in magnetictrip circuit breakers



ETiAL 3,189,707 COIL FORM ADAPTED FOR USE- IN MAGNETIC-TRIP CIRCUIT BREAKERS June 5 AR. NORDEN Filed April 3, 1962 FIG. I.

FIG. 2

INVENTORS ALEXANDER R. NORDEN TOMCZAK FIG. 4

BYFELIKS ATTORNEY United States Patent 3,189,707 COIL FORM ADAPTED FUR USE IN MAGNETIC TRIP CIRCUIT BREAKERS:

Alexander R. Norden, New York, N.Y., and Feiiks Tomczak, Newark, N.J., assignors to Federal Pacific Electric Company, a corporation of Delaware Filed Apr. 3, 1962, Ser. No. 184,202 12 Claims. (Cl. 200-88) This invention relates to coil forms and to circuit breakers having an electromagnet for effecting automatic release in response to an overload.

In order to provide sensitive magnetic tripping of small molded case automatic circuit breakers within the limited space available in the casing it is necessary that an extremely compact coil be employed. A flexible braid has normally been employed as a conductor between the coil and a portion of the breaker that is movable relative to the coil. To simplify breaker construction and to minimize the number of connections to be made therein, it is desirable to use the flexible braid as a winding about the coil form and thereby produce a tripping coil.

Accordingly, one object of this invention is to provide a novel circuit breaker having an improved tripping electromagnet that has a terminal lead of flexible braid. A related object resides in the provision of a novel electromagnet including a coil of flexible braid and a coil form that is specially adapted to retain the braid in its wound condition.

Another object of this invention is to provide a novel coil form having integral conductor retaining means.

A further object of this invention is to provide a coil form including integral means for retaining the coil form in position about its core.

A further object of this invention is to provide a coil form suitably equipped for reception and individual retention of separate convolutions of a flexible uninsulated conductor.

Yet another object of this invention is an improved circuit breaker magnetic tripping coil which utilizes the flexible braid otherwise employed as a connector between portions of the breaker and which is further characterized by the braid being wound about a winding-retentive coil form.

These and other objects and advantages will become apparent from a study of the specification in connection with the accompanying drawings in which:

FIG. 1 is a side elevation of an illustrative circuit breaker with one side wall of the casing removed to reveal the internal mechanism;

FIG. 2 is an enlarged elevation of a coil that constitutes part of the circuit breaker of FIG. 1, in partial crosssection along the line 22 of FIG. 3;

FIG. 3 is a left-hand end elevation of the coil form included in FIG. 2; and,

FIG. 4 is a top view of said coil form.

Referring to FIG. 1 there is illustrated a circuit breaker embodying one aspect of the invention. This circuit breaker is more fully shown and described in copending US. patent application Serial No. 122,822 filed July 10, 1961, which is assigned to the assignee of the present invention. The circuit breaker shown in the drawings has an enclosure comprising front and rear casing walls of insulating material. Only the rear casing wall 12 .is

illustrated for purposes of clarity. A pair of terminals 14 and 16 are mounted on opposite ends of the enclosure 10. A moving contact arm or carrier 18 is supported between its ends on a pivot spring 20. An operating handle 22 having a pivot 22a has bearings (not shown) in the opposite casing walls. Handle 22 is connected by a rigid U-shaped wire link 24 to a so-called bell-crank or pivoted actuator 26 that has an insulated pivotal bearing (not shown) at the right hand end of contact arm 18. A contact-opening spring 28 acts downward against a portion of contact arm 18 to the left of pivot 20 as seen in FIG. 1, thereby applying counterclockwise bias to the contact arm 18. Spring 28 also applies clockwise bias to handle 22 both in the open position illustrated and in its closed position at the left-hand extreme position allowed by the casing. Spring 28 thus applies sustained bias to handle 22 and contact arm 18 urging them in their respective oil or open positions. A depending portion 18a of the contact arm has an integral extrusion or pivot 18b that supports contact element 30. Contact portion 30:: cooperates with a corresponding contact 14a carried by the wire-connecting terminal 14. Contact portions 14a and 30a cooperate in a region of the casing which forms an arc chamber and has a vent 32 to the exterior.

A current-responsive bimetal 34 is joined by a rivet to the contact element 30 so that the bimetal and contact element form a unit that is pivotally supported by contact arm 18. A stop 10:: projects from the rear casing wall so as to underlie bimetal 34.

Another depending portion of the contact arm carries a coil 36 of flexible copper braid 37 welded to bimetal 34 near the right-hand extremity of the bimetal. The braid has an extension 38 that is united to plug-in terminal 16 of the circuit breaker. Coil 36 is formed about a coil form 48 of insulation, and the successive turns of the braid are separated from each other by the ribs 42 on coil form 40. The coil form fits tightly on the depending portion 180 of the contact arm of soft iron or other suitable magnetic material. The axial length of the core (not shown) is slightly less than that of the coil form 48, so that there is no danger of electrical contact being made between bimetal 34 and the core. The bimetal is of magnetic material, and acts as an armature that is attracted toward coil 36 when the latter is energized. A magnetic circuit is formed by the core, the portion of the contact arm that supports the core, and bimetal.

The circuit breaker may be closed by driving the operating handle 22 counterclockwise about its pivot to apply thrust to link 24 and in that way to bias actuator 26 clockwise to latched engagement with the bimetal 34, further operation of the handle causing clockwise movement of arm 18 and the parts carried thereby. This movement, as can be seen from the drawings, will result in contact portions 38a and 14a engaging. This degree of move ment causes relative motion between the coil 36, secured to the arm 18 and the adjacent stationary terminal 16 to which the flexible braid 37 is secured. In the event that a moderate overload current persists, the bimetal curves downward, and the actuator 26 is released so that spring 28 drives the contact arm 18 and contact 30acounterclockwise to open the circuit. Upon the passage of a current surge of sufficient magnitude through the coil 36, the bimetal is attracted toward the coil and disengages the actuator, causing the circuit breaker to be opened.

From the foregoing it can be seen that the coil 36 must be retained in its position in order to maintain the desired magnetic-trip characteristics of the circuit breaker. Additionally it will be seen that the coil and coil form must resist the forces applied to the braid by the movement of the contact arm 18, and the coil therewith, in relation to stationary contact 16. The end of coil 57 opposite 7 lead 38 is flexible and extends to the bimetal which moves in relation to the coil when the circuit breaker is tripped.

Coil 37 and terminal lead 38 are of bare braid, held in position by coil form 4b as shown in FIG. 2. The coil form 40 comprises an electrically insulating body that has a series of conductor-receiving grooves 44 defined by the ribs 42 of each end of the coil form. Opposed side walls 46 and 48 of each grooves are provided with confronting inwardly directed projections 50, 52 respectively, for retaining the conductor 37 in the groove.

The coil form 40 is made of nylon or similar insulating plastic that is preferably resilient. The coil form has a central aperture 56 for receiving a core that is part of the magnetic structure 18c. A depending portion 6d of the coil body is provided with an inclined, wedge-shaped projection 62. The coil form (with the coil thereon) is slipped down onto core 18c, wedge 62 and portion on of the coil form being laterally deflected at that time. When the coil form is fully in place, the shoulder 64 of the wedge snaps under a lanced edge of core l.8c,.to retain the coil form 40 in position. This depending portion 69 insulates flexible terminal lead 38 against contact with core 18c.

Groove 44 is formed in a helix about the central axis of the coil body 44 The helix has end segments 66, 63 which are in parallel planes perpendicular to the axis of the core passage 56. The plane-parallel portions 66, 68 are formed at the opposed ends of the generally rectangular coil form. Intermediate connecting groove segments 72, 74 (FIGS. 2 and 3) are inclined with respect to the coil form end plane. In this configuration the rib 42, which defines the groove d4, may be characterized as having a stepped pitch.

The projections and 52 extend inwardly from opposite side walls v4 6, 48 of the ribs 42 and substantially close the open end of the groove 44. The projections 50 and 52 are deflectable to provide clearance to admit the conductor 37 when it is forced therebetween during the coil winding operation. The size of the conductor 37 and the size of the groove are preferably related so that the conductor nearly fills the groove. Projections 50 and 52 constitute a constriction, so that, after 'winding, the coil is effectively retained in the groove.

While a single embodiment of the invention has been described in detail it will be readily apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.

What is claimed is:

1. In a circuit breaker including a release mechanism having a movable bimetal latch of magnetic metal, the combination of a coil form and a coil thereon spaced from said latch, said latch being magnetically attractable toward said coil to operate said release mechanism, a fixed terminal, means supporting said coil and said bimetal for operation as a unit in closing operation of the circuit breaker so that said coil moves relative to said terminal, said coil being formed of bare conductive braid extending continuously from said bimetal around said coil form and to said terminal, said coil form having ribs separating successive convolutions of the coil from each other and said ribs having projections overlying said convolutions for preventing the accidental unwinding thereof, said coil form having an endwise projection disposed lateral of said core and effective to insulate said conductor from a corresponding portion of said core.

2. In a circuit breaker having separable contacts, overload release means, and a magnetically attractable releasable member, the combination including a magnetic core,

7 a coil form on said core, said coil form comprising an electrically insulating body having a conductor receiving groove formed therein, the Walls of said groove having integral transverse projection for retaining a conductor in said groove, and a conductor wound about said coil form and retained therein by said projections, said coil being formed of uninsulated or bare conductive braid and extending to a part of the circuit breaker that moves relative to the coil in the operation of the circuit breaker.

3. A trip coil for a circuit breaker, said trip coil including a coil form comprising a body having integral ribs defining conductor receiving grooves, inwardly directed projections on said ribs, and a conductor retained in said grooves by said projections.

4. A coil comprising a body, a continuous conductor wound about said body, integral formations extending from said body to separate successive turns of said winding from each other, and integral projections on said formations overlying said conductor at spaced parts of the winding to prevent the unwinding thereof.

5. A coil comprising an electrically insulating body having a central core-receiving aperture, means integral with said body defining a conductor-receiving groove, at least one of the walls of the groove having a conductorretaining projection extending toward the opposite wall of the groove, and a conductor wound about said body and retained thereon by said projection.

6. A .coil form comprising an electrically insulating generally rectangular body having a central aperture and opposed end and sidewalls, a conductor receiving groove formed in said body, said groove being defined by a generally helical rib extending about said body perpendicular to said body, said rib having integral projections for retaining the conductor in said groove.

7. A coil form comprising an electrically insulating body having a central aperture therein, a conductor receiving groove formed in said body, said groovehaving opposed side walls, said side walls having inwardly directed projections for retaining conductor in said groove, said body having a portion projecting inwardly of said central aperture for retaining a core therein.

8. A coil form comprising an electrically insulating body formed from a resilient material, said body having a conductor receiving groove formed therein, said groove having opposed side walls projecting from said body, said side walls having inwardly directed deflectable projections for retaining a conductor in said groove, said projections substantially closing said groove.

9. A coil form comprising an electrically insulating body having a conductor receiving groove formed therein, said groove having opposed side walls projecting from said body, said side walls having inwardly directed deflectable projections for retaining aconductor in said groove.

10. A coil form comprising an electrically insulating body having a conductor receiving groove formed therein, said groove having opposed side walls, said side walls having inwardly directed portions for retaining a conductor in said groove.

11. A trip coil for a circuit breaker, said trip coil including a body having a central core-receiving aperture, means integral with said body defining a conductor-receiving groove, said groove being defined by a generally helical rib of stepped pitch extending about said body perpendicular to said body, said rib having integral projections for retaining a conductor in said groove, and a bare flexible braided conductor wound about said body in said groove and retained therein by said integral projections.

12. In an electromagnet' having an armature operable by said electromagnet, and a fixed conductive element,

said electromagnet including a magnetic core, the combination of a coil form on said core, and a conductor Wound about said coil form, said coil form comprising an electrically insulating body having a conductor-receiving groove formed therein, the Walls of said groove having integral transverse projections for retaining a conductor in said groove, and said conductor being retained in said groove by said projections, said coil being formed of flexible braid that extends integrally to said conductive element and is joined thereto electrically and mechanically, said electromagnet constituting a unit that is movable relative to said conductive element in the operation of the combination and said coil form serving to retain said coil in the desired configuration despite relative References Cited by the Examiner UNITED STATES PATENTS Re. 15,030 1/21 Steinberger et a1 336205 2,210,259 8/40 Sachs 200-116 2,312,169 2/43 Jackson 200-88 2,665,393 1/54 Bocciarelli 336198 2,937,251 5/60 Cellerini 20088 2,982,888 5/61 Whearley 336-205 OTHER REFERENCES German printed application 1,003,368, 1/52 (Seekamp).

motion between said electromagnet and said conductive 15 ROBERT SCHAEFER Primal? Examiner element.

BERNARD A. GILHEANY, Examiner. 

1. IN A CIRCUIT BREAKER INCLUDING A RELEASE MECHANISM HAVING A MOVABLE BIMETAL LATCH OF MAGNETIC METAL, THE COMBINATION OF A COIL FORM AND A COIL THEREON SPACED FROM SAID LATCH, SAID LATCH BEING MAGNETICALLY ATTRACTABLE TOWARD SAID COIL TO OPERATE SAID RELEASE MECHANISM, A FIXED TERMINAL, MEANS SUPPORTING AID COIL AND SAID BIMETAL FOR OPERATION AS A UNIT IN CLOSING OPERATION OF THE CIRCUIT BREAKER SO THAT SAID COIL MOVES RELATIVE TO SAID TERMINAL, SAID COIL BEING FORMED OF BARE CONDUCTIVE BRAID EXTENDING CONTINUOUSLY FROM SAID BIMETAL AROUND SAID COIL FORM AND TO SAID TERMINAL, SAID COIL FORM HAVING RIBS SEPARATING SUCCESSIVE CONVOLUTIONS OF THE COIL FROM EACH OTHER AND SAID RIBS HAVING PROJECTIONS OVERLYING SAID CONVOLUTIONS FOR PREVENTING THE ACCIDENTAL UNWINDING THEREOF, SAID COIL FORM HAVING A ENDWISE PROJECTION DISPOSED LATERAL OF SAID CORE AND EFFECTIVE TO INSULATE SAID CONDUCTOR FROM A CORRESPONDING PORTION OF SAID CORE. 